Voltage control challenges on weak grids with high penetration of wind generation: ERCOT experience

More than 9 GW of wind capacity has been connected to the Electric Reliability Council of Texas (ERCOT) grid. In order to accommodate the installation of future wind generation, the Competitive Renewable Energy Zone (CREZ) transmission expansion project has been planned. The CREZ project includes over two thousand miles of new 345kV transmission lines and is expected to be completed by 2014. Planning studies have been conducted to ensure that new wind generation can be reliably delivered to the ERCOT grid through the CREZ transmission facilities. Voltage oscillations and temporary overvoltage were observed in the CREZ system dynamic studies. Weak grid as indicated by low Short Circuit Ratio (SCR) was considered to be the primary cause for those voltage issues. This paper presents the analysis, including causes and solutions, for these voltage stability issues. An actual oscillatory response of an existing wind power plant (WPP) captured on a Phasor Measurement Unit (PMU) and its postevent analysis supported all the findings in the CREZ planning studies. Both the real time operation events and planning studies demonstrate the voltage stability impacts of high penetration of wind generation on weak grids.